Utilizing a computational approach, this study quantifies the onset of lubrication starvation for line contacts of rough surfaces operating under typical ranges of automotive gearing applications. The response parameter is selected as the critical film thickness supply, at which starvation initiates. The potential influential parameters (predictors) considered include normal force density, rolling velocity, sliding, lubricant viscosity, and surface roughness amplitude. A non-Newtonian thermal mixed lubrication model is employed to determine the critical lubricant supply under various operating and surface roughness conditions. General linear regression is implemented to reach an easy-to-use equation (R-squared value higher than 97%), facilitating the quantification of starvation dependence on the predictors that are statistically significant.
This study establishes the critical temperature of scuffing for contacts of gears made of AISI 8620 steel alloy, lubricated by Dexron 6 oil. Through thermal mixed EHL modeling, experimental scuffing failures are simulated to determine the associated maximum surface temperature, which consists of bulk and flash components. This temperature is referred as the limiting/critical temperature of scuffing, and is believed to be independent of operating conditions, while vary for different solid material and lubricant pairs [1-4]. It is found sump lubricant temperature rise affects surface temperature by contributing to the bulk component. The flash component is largely dictated by asperity interactions within contact zone, where Hertzian pressure is not an appropriate measure of micro-scale asperity contact loading. The observed scuffing scars are shown to be in good agreement with the high temperature zone predicted by the computational model.
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